The reconstruction of tracheobronchial defects which do not lend themselves to direct anastamosis is a problem of considerable magnitude. Although advances have been made in this area, a clinically reliable prosthesis which can be used to correct a variety of defects both intra-and extrathoracically has not been developed. Until now the demands for a flexible but noncollapsible, airtight, noniflammatory prosthesis which is incorporated in the host's tissues and most importantly lined with respiratory epithelium could not be met with a single prosthesis. Our preliminary studies have led to the development of composite prostheses consisting of porous high density polyethylene (PHDPE) rings and autogenous fibrocollagenous tissue which should be capable of fulfilling the rigid criteria for tracheobronchial replacements. The objectives of the proposed research are to evaluate 3 different types of composite prostheses which were developed in our laboratories and compare their performance. The prostheses will be used to reconstruct 5 cm. long circumferential defects in the cervical region of the canine trachea. The clinical performance of the prostheses will be determined by physical, radiographic, and bronchoscopic examinations. After 6, 12, and 24 months animals will be sacrificed and the prostheses subjected to gross and microscopic examination. The results of these examinations will be correlated with the clinical studies and comparisons will be made between the performance of the three types of prostheses.